Preparation of methyltrimethylolmethane



Patented Aug. 11, 1942 rnarm'rrois 2,292,926 ormzrnnrnnmrmon- Merlin M. Brnbaker, Wilmington, m4. and Ralph A. Jacobson, L du Pont de ton, Del.

N rmans. Application Landenberg, Nemours & a corporation of Delaware 7 Pa., aasignors to E; Company, Wilming-, v I

May 1 0, 1938,

Serial Nazo'auz 1Claim.(Cl.260835) This invention relates .to an improved method of more particularly 7 to an improved method for preparing this compound from formaldehyde and propionaldehyde. a

An object of this invention i to provide-an improved process of preparing methyltrimethylolmethane whereby good yields are obtainable. A more particular object is to provide an improved method fol-"preparing this compound from. ro-

pionaldehyde and formaldehyde, and for isolating the product in an eifective manner from the reaction mixture.

vention. 3

The above objects are accomplished by reacting proprionaldehyde with aqueous formaldehyde in the presence of alkali and distilling the prodnot with superheated steam" in a vacuum, whereby the methyltrimethylolmetbane is obtained in pure form and good yield. Itfis desirable, prior to the vacuum steam distillation, to subject the crude initial condensation product to one or more preliminary purification treatments, which are characterized hereinafter.

If a mixture of aqueous formaldehyde and Y propionaldehyde is slowly treated with solid caustic alkali, beginning at a controlled low temperature, e. g., to 10 C., a colorlesssyrup is obtained containing a high 'jyield of methyltrimethylolmethane. The reaction by which this compound-is formed is illustrated by the following equation, sodium hydroxide representing the caustic alkali: V

cm cmoH+rioooNa HIOH After production of the methyltrimethylolmethane-a hydroxide mixture in the. isolation of this flcult problem, We have now found that this problem may be overcome by subjecting the mixture to vacuum distillation with superheated steam. The steam is suitably heated to 200 to 300 0., though temperatures outside this range are not precluded. In practice, it is desirable, before proceeding with the latter distillation, first to subject the crude reaction product to ordinary vacuum distillation in order to remove lower boiling impurities which are present, thereby leaving a mixture of alkali formate and methyltrimethylolmethane to be separated by th vacuum,

preparing methyltrimethylolmethane, and

Other objects'will be apparent from the ensuing description of the insuperheated steam distillation. This ordinary vacuum distillation is also desirably in turn preceded by. treatment ofthe crude initial conden-' vsation product with the calculated amount of s sulfuric acid, whereby the alkali formate is converted to alkali sulfate. apart of which separates and ma be filtered on- This preliminary con-- version ofalkali formate to alkali sulfate, and the partial removal of the latter, is advantageous particularly with those types or stills where a large amount of alkaliformate might ofle'r obstruction -to-;the passage :of steamr The final mixture to be separated by the vacuum, 'super- I heated steam distillation, of course, consists-in this. instance of methyltrimethylolmethan and l alkali sulfate ratherthan formate. 1

The above treatments prior to the vacuum superheatedsteam distillation, while the enablethe process involving the latter distillation to be carried out with better results, are not obsolutely I essential, and, with or without them, the mentionedtype ofsteam distillation enables the production of pure methyltrimethylolmethane inexcellent yields, the diillcultly removable alkali formate or sulfate, as the case may be, remaining ,asaresidueinthe still,

Commercial formalin (37% aqueous formalde hyde), is a convenient, satisfactory and economical source of formaldehyde, but paraf0rmalde-' aohyde or trioxymethylenemaybe used'lf desired.

The caustic alkali may beuse'd in solid form (sticks, ilakes,'or pellets) or as an aqueous solution. Any metal hydroxide ;is suitable, sodium hydroxide being preferable from. the

as standpoint of cost and potassium hydroxide from:

the standpoint ofthe greater solubility of the re sulting potassium formate with attendant greaterfacilityin the'steamdistillation;

In the preliminary purification step wherein so the crude reaction product'is treated with sulfuric-acld', the .latter acidmay be replaced by any other. strong inorganic.acid,'such as hydro chloric, phosphoric or nitric acids. These acids, however, :are in general less satisfactory than sulfuric becauserthe resulting salts are ingen eral more soluble than sodium sulfate in the reaction medium. An acid which forms an insoluble or only partially soluble salt is preferred. The reaction is preferably begim at a relatively low temperature, 1. e., around 10 (3., because shortly after addition of potassium or sodium hydroxide is started, a strong exothermic reaction takes place resulting in a sudden temperature rise. Although the temperature may rise to 00' 66 or 70 0. without apparent harm as far as yields and metlrvltrimethylolmethane.

are concerned, there is danger of loss of material and effective cooling is desirable in order to keep the reaction under control. Accordingly, we normally prefer at this stage to keep the temperature at about 30 C. or less.

The time for the initial reaction is largely gov- 'erned by the rate of addition of the alkali and the rate is in turn governed by the effectiveness of the cooling system, but in general from 3 to 6 hours is required;

The excess water, formaldehyde and low boiling constituents of the reaction mixture can be removed by evaporation, distillation or by vacuum distillation, although we prefer to remove them by vacuum distil1ation since the operation can be accomplished in a shorter time and to a more complet degree. The residue left from this distillation is a mixture of alkali formate For the separation of these two products the steam -distillation with superheated steam is best'carried out at a temperature of about 250 C. and a vacuum of about 40 mm., though other pressures and temperatures may, of course, be used. The pressure and temperature, as those skilled in the art will understand, must be co-adjusted. For example,

if the pressure is in the range of 2 to 25 mm.,

the temperature'can be reduced to 225 C. with equally desirable nesults.

For the reaction itself, any type of vessel provided with a stirrer and a means of cooling can be utilized. For the distillation, any of the usual types of equipment for vacuum distillation can beemployed provided that means for uniformly heating the kettle and for introducing superheated steam are provided. However, since large amounts of alkali formate are left as a residue, the most satisfactory type of still is one in which the mixture of alkali formate and methyltrimethylolmethane remaining after distillation of the, more volatile constituents is fed onto hot rolls under reduced pressures. The methyltrimethylolmethane is thereby volatilized by a flash distillation while the alkali formate remains on the rolls and is continually removed therefrom by a scraping. device.

The following examples, in which parts are by weight, illustrate more exactly how the inven tion is practiced.

' Example I perature is maintained below 30 C. This operation requires about 6 hours. The mixture is then submitted to vacuum distillation at about 60 mm. pressure, while steam is slowly passed into the mixture. By this procedure, water, unreacted formaldehyde and small amounts of volatile byproducts are distilled out leaving a mixture of sodium formate and methyltrimethylolmethane in the still pot. The pot is then heated to 250 C. by circulating hot oil through the jacket formerly used for cooling, and superheated steam is passed into the mixture of sodium formate and methyl trimethylolmethane, while maintaining a vacuum on the system of 40 to mm. By this procedure the methyltrimethylolmethane is volatilized, passesthrough a short heated pipe and collects in a series of two condensing vessels surrounded by water, the temperature of which can be regulated. Most of the methyltrimethylolmethane condenses in the first condensing vessel, the remainder being stopped by the second condenser. A total of 4770 parts (79.5%) of methyltrimethylolmethane is obtained. This product is sufficiently pure for most purposes but it may be crystallized readily from acetone to give analytically pure crystals melting at 198-199 C. The sodium formate remains in the still pot.

Example II formaldehyde solution and 2900 parts of propionaldehyde is treated slowly with 2000 parts of solid sodium hydroxide as described in Example I. The reaction mixture is then treated with dilute sulfuric acid containing 2250 parts of actual sulfuric acid. The latter converts the sodium formate in the mixture into sodium sulfate which, being less soluble in the solution than sodium formate, separates in. part from the solution. The sodium sulfate which precipitates is filtered ofi and the filtrate then distilled as in Example I, the easily volatile constituents being first distilled by gentle heating in a vacuum and the methyltrimethylolmethane being finally volatilized by heating the still pot to 250 C. and passing in superheated steam. The methyltrimethylolmethane is obtained inthe condensers as in Example I and amounts to 4914 parts or 81.7% of the theoretical.

Although acetone has been described in the examples as the preferred solvent for recrystallization of the methyltrimethylolmethane, other ketone-type solvents, such as methyl ethyl ketone are also satisfactory and may be substituted for the acetone. Ester-type solvents, such as butyl acetate are also suitable.

Various changes may be made in the details and operation of the present invention without departing therefrom or sacrificing any of the advantages thereof.

We claim:

In a process for producing methyltrimethylolmethane by reaction of formaldehyde and propionaldehyde, the step which comprises carrying out the reaction in the presence of an alkali metal hydroxide, converting the alkali formate in the reaction product to alkali sulfate, removing the sulfate which separates, and removing by vacuum distillation volatile impurities boiling lower than methyltrimethylolmethane, and isolating methyltrimethylolmethane from the residue by distilling in vacuo with superheated steam. MERLIN M. BRUBAKER.

RALPH A. JACOBSON. 

